(RNN) - Doctors are sick less often than restaurant workers. Accountants miss more work than managers. Barbers, waiters and police officers miss the most of all, about one day every two months.

A survey by Gallup and Healthways ranks professions based on how many sick days they take each year. The U.S. economy loses billions a year because of sick days.

It makes sense that people can't work when they are not well.

But some unhealthy professions are the least likely to call in sick. Foresters, farmers and workers in the fishing industry miss only marginally fewer days than doctors, but they are the most likely to be in poor health, according to a story in Thinkstock.

Meanwhile, nurses, clerks and service workers are healthier than most but are the most likely to call in sick.

Workers who don't get paid if they don't come to work, workers with low income or with less job security are also unlikely to call in sick.